1. Field of the invention
This invention relates to a process and an apparatus for drying a coated web such as photosensitive materials for photographic purpose (photographic photosensitive materials).
2. Description of prior art
Various photographic, photosensitive materials and other materials are manufactured by drying a continuous web such as a plastic support or a paper support on which one or more coating compositions are applied. This composition is generally produced by dissolving or dispersing prescribed components in an organic solvent. The coated web is dried by blowing hot air or irradiation by infrared light. In such drying methods, when the concentration of the organic solvent vapor becomes high, an explosion occurs. Therefore, a large quantity of air was introduced into the oven, and thereby the concentration of the organic solvent vapor was controlled so as to be kept lower than one third of the explosion limit. As a result, a lot of thermal energy was consumed for heating of the air for dilution and for incineration of a large amount of the exhaust gas, and evaporation of the solvent. Various investigations for solving this problem have been made, and for example, recovery of heat of the exhaust gas by using a heat exchanger and a method of using water as the solvent have been proposed.
On the other hand, it is known that, in the drying process of continuous coating on a metallic strip, an explosion of a solvent is prevented by blowing a hot inert gas into an oven and thereby the air for dilution is not added (USP No. 3,909,953). In this method, the exhaust gas is mixed with air, and organic solvent in the gas is incinerated to produce an inert gas. Heat of the inert gas is utilized for the drying of the metallic strip by returning the incinerated gas into the oven, and excess heat is recovered by a heat exchanger and utilized.
In the recovery of heat of the exhaust gas by using a heat exchanger, yield of heat recovery is usually about 50 to 60%, and cost of equipment is expensive because a big heat exchanger is necessary. In the method of using water as the solvent, consumption of thermal energy is increased by evaporating the water to the contrary. In the foregoing method to incinerate the exhaust gas, cost of equipment is expensive because a big incinerator and heat exchanger are necessary, and it is also a problem that whole amount of the organic solvent which is valuable is incinerated.